Method of preventing supersaturation of electrolytes with arsenic, antimony and bismuth

ABSTRACT

A method of preventing supersaturation of electrolytes with arsenic, antimony and bismuth in which the electrolyte solutions are contacted with stannic acid and the stannic acid is regenerated with electrolytically produced sulfuric acid having a higher concentration than the sulfuric acid in the electrolyte. The regeneration of the stannic acid chemisorbent is carried out in the same adsorber as the adsorption and using floating adsorbent particles in a bath.

United States Patent 191 *June 3, 1975 Schulze METHOD OF PREVENTINGSUPERSATURATION OF ELECTROLYTES WITH ARSENIC, ANTIMONY AND [21] Appl.No.: 352,079

[30] Foreign Application Priority Data Apr. 19,1972 Germany 2218934 [52]U.S.Cl. Q. 204/130; 204/93; 204/108; 210/34;2l0/36;210/38 [51] int. Cl.501a 15/06 [58] Field of Search 204/108, 93, 130; 210/30, 210/32, 34,36, 38; 423/522, 53]

[56] References Cited UNITED STATES PATENTS 489,632 1/1893 Gruessner204/108 2,793,183 5/1957 Thurman 210/34 2,798,040 7/1957 Pye et a1.-204/108 2,888,390 5/1959 Lapee 204/108 3,536,615 10/1970 Bunn r 210/363,547,810 5/1968 Cooper 210/30 3,676,357 7/1972 Ciuti et al. 210/363,696,012 10/1972 Schu1ze..., 204/108 3,755,161 8/1973 Yokota et a1.210/36 Primary Examiner-Samih N. Zaharna Assistant Examiner-IvarsCintins Attorney, Agent, or Firm-Karl F. Ross; Herbert Dubno [57]ABSTRACT 4 Claims, 1 Drawing Figure METHOD OF PREVENTING SUPERSATURATIONOF ELECTROLYTES WITH ARSENIC, ANTIMONY AND BISMUTH FIELD or THEINVENTION The present invention relates to a method of'prevenb ingsupersaturation of electrolytes-with arsenic, antimony and bismuth andrepresents an improvement over the system described and claimed'in mycommonly assigned US. Pat. No. 3,696,012.

BACKGROUND OF THE INVENTION In the aforementioned patent, I describe aprocess for preventing excessive accumulation of arsenic, antimony andbismuth in electrolytes used in the electrolytic refining of non-ferrousmetals, especially copper, the process involving the adsorption 'of theimpurities upon a chemisorbent in the form of a low-soluble metal-oxidehydrate,'namely stannic acid, stable in the presence of sulfuric acid.

In the patent I point out that, in the electrolytic refining ofnon-ferrous metals, especially copper, solubilization of the anodecontaining the impure'me'tal gives rise to accumulation in the solutionof electrolytes of one or more impurities from GROUP V (A) of thePERIODIC TABLE, namely arsenic,a'ntimony and bismuth. These impuritiescreate various difficulties.

Depending on the nature of the deposit and upon the process conditions,in the electrorefining of copper by electrodeposition upon a cathode ofcopper from a solution and the solubilization of impure copper from ananode, the cathodes produced contain undesirable impurities includingthe GROUP V (A) elements, namely arsenic, antimony and bismuth togetherwith lead, nickel, selenic and other impurities. The presence of theseimpurities in the cathode, where they contaminate the end product of theelectrolytic refining process, arises because the electrolyteso'lubilizes these elements from the'anode slime and carries thesecomponents of the anode slime to the cathode surfaces, the impuritiesbeing trapped in the growing cathode. To an extent, moreover, theimpurities may be incorporated in the cathode from solution orelectrolyte which is mechanically received, e.g. in capillary cracks inthe electrode, in interstices or openings such as the space between themetal of the cathode and the supporting loops, etc. Finally, saturationof the electrolyte with antimony and bismuth eventually gives rise tothe formation of precipitates which can be incorporated mechanically inthe growing cathode. i

It has, therefore, long been a problem recognized in the art, thatexcessive concentrations of antimony, arsenic and bismuth inelectrolytes for the electrodeposition of nonferrous metals may causecontamination of the end product and difficulties the regeneration orprocessing of the electrolytes.

It is known, for example, that solutions such as the aforementionedelectrolytes become saturated with the afore-described impurities andform slimes or precipitate earlier when arsenic is present, sincearsenic leads to the formation of so-calledfloating slimes.Precipitation will also occur rapidly after the solution is saturatedwith calcium sulfate. Moreover, the solubility of salts of theimpurities is known to decreaseQ-with de It is consequently deposited asa precipitate in the drains and conduits of the tanks, the depositsbeing extremely hard and difficult to remove. In fact, they have astone-like character and may have thicknesses in excess of somecentimeters. The deposits may include. for example, 2 percent by weightbismuth, 18 percent by weight arsenic and 48 percent by weight antimony.In practice, replacement of the drains, pipes, fittings and conduitsisrequired periodically at considerable cost.

It is also obvious that the dangers which arise with increase in theproportions of antimony and bismuth in the electrolytic refining ofcopper, themselves increase with increasing transfer of these elementsfrom the anode into the electrolyte. On the other hand, there is thetendency to produce anodes which avoid these impurities, therebyincreasing the cost of the raw materials of the electrolytic refiningprocess. There is also the fact that low concentrations of the impurityelements in the electrolyte permit the electrolytic refining process toproceed more efficiently. It is not a practical solution to increase thepurity of the anodes since economical and technological considerationsin the pyrometallurgical level have been found to limit such purity.

As a result, the art has determined that various measures should befound for the electrorefining copper containing large proportions ofantimony and bismuth, i.e. high-antimony and high-bismuth copper. Inthese processes, the electrolyte is processed to keep the antimony andbismuth levels below saturation. If the amounts of the impurities arelow, it is merely necessary to use the processes which have beenemployed to recover nickel from a copper-containing electrolyte. In thisprocess, high nickel electrolyte is discarded'and 'low nickelelectrolyte is supplied to the refining tank,

OBJECTS THE INVENTION It is the principal object of the presentinvention to provide a process for preventing saturation of anelectrolyte with arsenic, antimony a-nd bismuth which extends theprinciples set forth in the aforementioned patent and improves thereon.

Another'object of the invention is to provide an improved process forcontrolling the buildup of antimony, bismuth and arsenic in anelectrolyte for the processing of non-ferrous metals, especially copper.

Another object of this invention resides in the provision of a processfor preventing supersaturation of coppperelectrowinning electrolyteswith members of GROUP V (A) of the PERIODIC TABLE.

Still another object of the invention is to provide an improved methodof operating a system for the electrorefining of copper from anodescontaining antimony,

bismuth and arsenic in amounts exceeding the acceptable limits of theseelements in the cathode.

Another object of the invention is to provide an economical method ofremoving members of the GROUP V (A) series of elements of the PERIODICALTABLE from'acid electrolytes as obtained in the electrolytic refining ofcopper.

SUMMARY OF THE INVENTION These objects are attained, in accordance withthe present invention, by a modification of the aforedescribed systemwhich enables recovery of the impurities without introducing otherimpurities into the process. Essentially, the invention is carried outby regenerating the chemisorbent in the same adsorber or adsorbers asthe adsorption step is carried out originally. The adsorbent floats, inaccordance with the invention, and the adsorption and regeneration stepsare carried out with floating adsorbent particles, the sulfuric acidrequired to regenerate the chemisorbent being circulated andregenerated, in turn, in an electrolytic unit which is included in thesulfuric acid recirculation path. As a result of the electrolyticregeneration of the sulfuric acid, the amount of sulfuric acid requiredto regenerate the adsorbent is reduced (owing to the low solubility ofthe impurities) and the impurities themselves are recovered in a highconcentration in elemental form.

The process of the present invention thus comprises removing fromelectrolyte solutions, especially solutions used in theelectrolytic-copper process, the impurities arsenic, antimony andbismuth substantially continuously with their introduction into theelectrolyte with a large-surface chemisorbent which may float in theelectrolyte (preferably the chemisorbent is or includes stannic acid)and regenerating the stannic acid with sulfuric acid of a higherconcentration than the sulfuric acid in the spent electrolyte.

The regeneration is carried out with agents which remain in theadsorbers or acid cycles and need not be separately treated and undersuch conditions that the adsorption apparatus may be relatively small.

It is an important aspect of the present invention that the adsorbent isfloated upon the solutions with which it is to be contacted, i.e. theelectrolyte to be treated by the adsorbent and the acid used to treatthe adsorbent, while both adsorption and regeneration are carried outwith the floating adsorbent particles. This affords the advantage thatliquids can be passed at a higher velocity from above through theadsorber or adsorbers because the floating particles provide virtuallyno resistance to such floating. Each of the liquids which is passedthrough the adsorber can be substantially completely removed therefromwithout significant rinsing so that there is virtually no mixing of thedifferent solutions. This is particularly important because theelectrolyte carrying the impurities and the regenerating sulfuric acidare passed through the adsorber or adsorbers alternately to depositimpurities upon the adsorber and strip the impurities therefrom insuccessive half-cycles. Air can be blown through the adsorbent,according to the present invention, although substantially no air isretained after a change of liquids. Where stationary porous substancesare used, on the contrary, the retention of air in pockets or by surfaceadhesion reduces the effective surface area and the capacity. Inaddition, retained air in these latter systems obstructs the passagesthrough the porous body and thus the flow of liquid through the system.

According to another feature of the invention, the chemisorbent isprovided in a layer which is coated onto a floating support togetherwith layer-forming or film-forming materials. The supports arepreferably particles of a foamed synthetic resin, especially polystyreneor polyurethane and the film-forming material is preferably a substancehaving a high wear resistance, high capacity (for the reaction andadsorbent) and a high degree of activity, when combined with thereactant, so that the layer possesses a high reaction rate. It goeswithout saying that the film-forming substance must also have highchemical stability and adhesivity or bond strength, being able to bondeven the peptizable chemisorbents. These requirements are met by the useof film-forming binders which have heretofore been employed as paints orcoatings for preventing access of a corrosive environment to a protectedsurface. It is indeed surprising that the high reactivity layer, whichis used in accordance with the present invention, may make use ofcompositions which have hitherto found their principal utility inpreventing chemical or physical-chemical activity.

The coating, preferably, comprises a solution or suspension of thechemisorbent in a mixture of binders, at least one of which acts as aflocculating agent for the reactant. The solution or suspensioncontaining the mixture is used to coat the supports and, after drying,forms a tough, firmly adherent and swellable film which contains thereactant (i.e. the chemisorbent).

Best results have been obtained with a binder system consisting of amixture of binders including a waterinsoluble component or a componentwhich swells only slightly in the presence of water and which impartstoughness and adhesive strength to the mixture. Another component whichis soluble or swellable in water and which, when combined with thewater-soluble component, is substantially insoluble in water so as to beretained in the coating after drying and renders the coatingsufficiently permeable to access solutions to allow access of thereactant in the coating to the solution to be treated thereby or used totreat the reactant.

The water-insoluble synthetic resin material, which may be used inalkaline and acid solutions, may be any of those hitherto employed aslatex paint vehicles. Preferably, the water-insoluble components is anacrylic ester in the form of the homopolymer or of polymers with vinylester, styrene, vinyl esters, vinyl chlorides or vinylidene chlorides.The soluble or swellable component of the binders, which is locked intothe film so as to be insoluble but as to contribute to the permeability,is preferably a flocculating agent of the polyacrylate, polya'crylicester, polyacrylamide, acrylic acid copolymer or polyethylene iminetype. The mixing ratio between the water-insoluble synthetic resincomponent and the water-soluble or water-swellable synthetic resincomponents (which is rendered insoluble in the film) may vary withinwide limits and depends only upon the ultimate properties desired in thefilm. For films of higher hardness or "greater toughness and lowerpermeability, the water-insoluble binder component may be increased inproportion whereas, for greater permeability, the proportion ofwater-soluble and water-swellable binder components (insoluble in thefilm) will be present in greater proportion. The water-soluble syntheticresin generally should make up 0.1 to 5 percent by weight, preferably 1percent by weight, of the binder components, based upon the amount ofwater-insoluble 'resins, while the remainder may also consist of 10 to1,000 percent by weight, preferably 200 percent by weight ofwater-swellable resins based on the amount of water-insoluble syntheticresin. The resulting coating has been found to have a satisfactorypermeability and air resistance. It is thus desirable to usewater-soluble and water-swellable synthetic resin materials incombination.

The activity of the coating may be increased by the addition of solubleor insoluble substances to the solution or suspension forming thecoating. These substances can be removed by solubilization and/ordecomposition, e.g. into a gas, once the coating has been formed uponthe support to leave pores in the coating to promote the reaction. Thesubstance which may be used to form the pores includes substances whichmeet the aforementioned solubility requirements, e.g. simple organiccompounds such as sugar, urea and the like, simple organic or inorganicsalts, especially sodium and potassium salts such as chlorides,sulfates, acetates and oxyllates, substances which have thermaldecomposition temperatures within the stability range of the coating-andproduce gas upon heating such as the hydrogen carbonates and. carbonates(especially of the alkali metals and the alkaline-earth metals), chalkand dolomite. or sulfites. The hydrogen carbonates and carbonates yieldcarbon dioxide upon heating while the sulfates generate sulfur. dioxide.Mixtures of' these poreforming substances may be used and the upperlimit as to the proportion of the pore-forming materials is establishedonly by the mechanical stability of the film, ie the maximum proportionof the poreforming material should be such that the film does not loseits cohesion. It is preferred to use about 5 percent by weight of thesoluble or low-solubility substances from this group and 50 percent byweight of insoluble substances based on the total content of the drybinder.

With systems of the type described it has been found that viscositycontrol is important to provide a filmforming or smooth-coatinghomogenous deposit and that it may be necessary to add viscositymodifiers such as monomeric or polymeric amines and amino alcohols toeliminate the film-forming or homogenous character of the coatingcomposition. These materials, which also serve as plasticizers, may beused in amounts up to 1,000 percent by weight based upon thewaterinsoluble synthetic resin component.

DESCRIPTION OF THE DRAWING The above and other objects, features andadvantages of the present invention will become more readily apparentfrom the following description, reference being made to the sole FIGUREof the drawing which shows a system for carrying out the presentinvention.

SPECIFIC DESCRIPTION A pump 2 withdraws enriched solution from acollecting box 1 through a conduit 3 and supplies the solution into abox 4 provided with an overflow weir 5. A conduit 6 connected to theupper portion of the box 4 continuously returns a major part of thesolution back into the collecting box 1. In spite of the long pipeline3, fresh solution from the box 1 will always be available at a suitabletemperature in'the overflow box 4 if the solution is recycled through 6at a sufficiently high rate.

Solution is supplied to an absorberl9 through a conduit 7 and a valve 8.The floating active mass 12 is disposed between flange-connectedsieveplates 10.

Filter cloths 11 having a suitable mesh size may also be used asretaining means, if desired. The air from the adsorber 12 can escapethrough a venting conduit 13. To ensure that the adsorber 12 remainsalways filled with solution, the adsorptively treated solution isreturned into the collecting box 1 through a conduit 14, whichconstitutes a siphon, a draining funnel 15, a valve 16, and a conduit17.

When the adsorption has been terminated, the valve 8 is closed and avalve 18 is opened so that the solution is drained from the adsorber.Rinsing water is supplied through a valve 19 into the collecting box Ior can be separately withdrawn through l4, l5. and a valve 20. Therinsing water will be drained when 19 is closed and 18 is opened.

Valves 21 are opened to initiate the regeneration of the adsorber mass12. Sulfuric acid now flows into the adsorber and through 14, 15 and avalve 22 into a drain container 23. A heater 24 heats the acid to thedesired temperature. Under control of a float switch 25, a pump 29discharges the acid through a valve 26 and conduits 28 and 30 into theelectrolytic cell 33, which is provided with insoluble anodes 31 andwith cathodes 32. Only one anode and one cathode are shown.

It may be desirable, for instance, to use anodes of lead and cathodes ofcopper. The shape of the cathodes is not critical. They may consist ofplates, rods, tubes, perforated plates or the like. Where plates areused, however, it will be recommended to immerse only narrow webs intothe solution for a supply of current so that the gas-laden, floating mudwhich has been formed at the cathode can be carried without obstructiontogether with the draining acid through an outlet 34 onto a filter 36.All conventional units may be used as filters because the mud can befiltered well. Any acid which is supplied in excess is not filtered butis conducted over an overflow 35 into a reservoir 38.

When the regeneration has been terminated, 21 is closed and the valve 18and a valve 37 are opened so that the float switch 25 ensures that theacid can be completely drained from the absorber and collected in thereservoir 38 even if there is no sufficiently large difference betweenthe levels of the adsorber and drain container. When the float switch 25is disconnected and the valve 27 is opened, the electrolysis of the acidcan be continued in a separate cycle. Bottom sludge in the electrolyticcell 33 is fed through a bottom pipe 39 onto a filter 40. The acid whichis carried along flows through a conduit 41 into the tank 38. In thisway, the electrolyte solution can be purified only in an operation whichis interrupted for the regeneration of the adsorbent mass. This is nodisadvantage in many cases because during the time for which theadsorption is interrupted the collecting box 1, owing to its highcapacity, can be filled to such an extent and the purity of theelectrolyte solution contained in said box can be adjusted so that thetime required to regenerate the chemisorbent is bridged. Alternatively,a second adsorber may be provided and the two adsorbers can operate inalternation so that the adsorption need not be interrupted.

SPECIFIC EXAMPLES EXAMPLE I 0.2 kilogram of a flocculating agentconsisting of polyacrylamide are dissolved in 20 kilograms of alowviscosity dispersion (25 percent) of an acrylate copolymer which isconventional as a paint vehicle. 20 kilograms diethanolamine are addedto the viscous, filament-forming solution to render it spreadable. Thismixture and 40 kilograms of a high-viscosity dispersion of an acrylicester copolymer conventional as a paint vehicle, 50 kilograms calciumstannate, l kilogram sodium hydrogen carbonate and kilograms prefoamedStyropor P 455 (polystyrene) beads are intimately blended until auniform sticky coating has been formed on each Styropor particle. Thematerial is dried in loosened layers at temperatures up to about 100C.The process can be considerably accelerated even at a low temperature bya circulation of air. the use of a vacuum, and tumbling. It will behighly desirable to tumble and at the same time to supply warm airthrough the tumbling mechanism.

Together with or without the supports on which the .material is driedand which consistof paper, sheet coated particles in the working media,any desired insoluble substances, preferably barite or lead sulfate, maybe admixed in the required amount to the mixtures.

EXAMPLE 4 100 grams stannic acid on polystyrene beads treated as aboveto contain calcium stannate and reformed into stannic acid as describedin the aforementioned patent this stannic acid is designated A in Tablel were charged into 100 liters of a warm copper-refining electrolyticliquor at a temperature of 60C, the electrolyte being drawn off from theadsorber in which the stannic acid/foamed polystyrene floated. Thetemperature was maintained constant during these steps. The residueretained in the adsorber is designated B in Table l. The duration of theentire process was only A; hour. The conditions and results of theexperiment are stated in Tables 1 and 2. The moisture values are notcharacteristic because they will obviously depend on the degree ofelimination of electrolyte. The stannic acid was regenerated bycirculating sulfuric acid downwardly through the floating particles.

Table 1 Substance A B A (grams) B (grams) B-A (grams) Amount 100 133.533.5 Moisture 55.9 31.9 55.9 42.6 1 3.3 Sn 27.4 20.5 27.4 27.4 0 As 0.315.0 0.31 6.69 6.38 Sb 1.0 11.7 1.0 15.6 14.6 Bi 0.009 0.85 0.009 1.141.13 Cu 0.03 0.46 0.03 0.62 0.59 Ni 0.08 0.107 0.107 Se 0.11 0.114 0.110.152 0.042 Fe 0.05 0.04 0.05 0.054 0.004 Ca 0.02 0.04 0.02 0.054 0.034

Table 2 Cu Ni As Sb Bi H lnitial liquor, grams per liter 39.7 20.5 7.20.48 0.05 165 Final liquor, grams per liter 39.7 20.5 7.1 0.33 0.04 165Difference, grams per liter O.l 0.l5 0.0l -l.4 -3l.3 20

Difference, 7r

The end of the reaction is indicated by a change in color from gray toyellow. When washed with water, the mass is ready for use and willresist even percent sulfuric acid at C.

EXAMPLE 2 The same mixture is prepared as in Example 1.

In this case, 0.2 kilogram flocculating agent consist= I ing ofpolyacrylamide are added as an aqueous solution of 1 percentconcentration. 2 kilograms, polyethylene imine are added to thicken themixture.

EXAMPLE 3 The same mixture is prepared as in Example 1.

In this case, 1 kilogram sodium hydrogen carbonate as a pore-formingagent is replaced by a mixture of 0.5 kilogram sodium hydrogencarbonate, 10 kilograms chalk and 2.5 kilograms common salt.

When it is desired to reduce the buoyance of the EXAMPLE 5 Anode coppercontaining 0.1 percent antimony and 0.015 percent bismuth was processedat a rate of metric tons per day. The electrolyte was constantly treatedwith floating stannic acid particles (as described) in a separateadsorber plant and was then returned into the electrolytic cycle. l.lmetric tons of tin in the form of stannic acid was used in this process,by

which the concentration of impurities in the electrolyte was held at 0.1gram antimony per liter and 0.035 gram bismuth per liter. In thisprocess. no floating slime and not deposits on the pipe walls of theelectrolyte conduit system were observed. The regenerating acid wasrecirculated H 80 l claim:

1. A process for preventing supersaturation of an electrolyte with animpurity selected from the group which consists of arsenic, antimony andbismuth which comprise the steps of:

a. treating said electrolyte with floating particles of a chemisorbentadapted to take up said impurity in an adsorber;

b. draining said electrolyte from said adsorber;

c. circulating a regenerating solution through said adsorber and intocontact with said floating particles to strip said impurity therefrom;and

d. electrolytically regenerating said solution along the circulatingpath thereof; wherein said chemisorbent is stannic acid, saidelectrolyte is a sulfuric acid electrolyte for the electrolyticallyrefining of copper and said regenerating solution is sulfuric acid moreconcentrated than said electrolyte.

2. The process defined in claim 1 wherein said particles are formed bycoating said chemisorbent in a filinforming binder system onto foamsynthetic resin particles.

3. The process defined in claim 2 wherein said particles consist of aresin selected from the group which consists of polystyrene andpolyurethane and said binder system comprises a water-insoluble bindercomponent selected from the group which consists of polymers of acrylicacid, homopolymers and copolymers of acrylic esters with vinyl esters,styrene. vinyl ethers. vinyl chloride and vinylidene chloride. a furtherbinder component serving as a flocculating agent for said chemisorbentand selected from the group which consists of polyacrylates, polyacrylicesters, acrylic esters copolymers, polyacrylamides and poly-ethyleneimines.

4. The process defined in claim 3 wherein said system further includesat least one component removable upon formation of the film, saidprocess further comprising the step of removing said removable component

1. A PROCESS FOR PREVENTING SUPERSATURATION OF AN ELECTROLYTE WITH ANIMPURITY SELECTED FROM THE GROUP WHICH CONSISTS OF ARSENIC ANTIMONY ANDBISMUTH WHICH COMPRISE THE STEPS OF: A. TREATING SAID SLECTROLYTE WITHFLOATING PARTICLES OF A CHEMISORBENT ADAPTED TO TAKE UP SAID IMPURITY INAN ADSORBER; B. DRAINING SAID ELECTROLYTE FROM SAID ADSORBER; C.CIRCULATING A REGENERATING SOLUTION THROUGH SAID ADSORBER AND INTOCONTACT WITH SAID FLOATING PARTICLES TO STRIP SAID IMPURITY THEREFROM;AND
 1. A process for preventing supersaturation of an electrolyte withan impurity selected from the group which consists of arsenic, antimonyand bismuth which comprise the steps of: a. treating said electrolytewith floating particles of a chemisorbent adapted to take up saidimpurity in an adsorber; b. draining said electrolyte from saidadsorber; c. circulating a regenerating solution through said adsorberand into contact with said floating particles to strip said impuritytherefrom; and d. electrolytically regenerating said solution along thecirculating path thereof; wherein said chemisorbent is stannic acid,said electrolyte is a sulfuric acid electrolyte for the electrolytIcallyrefining of copper and said regenerating solution is sulfuric acid moreconcentrated than said electrolyte.
 2. The process defined in claim 1wherein said particles are formed by coating said chemisorbent in afilmforming binder system onto foam synthetic resin particles.
 3. Theprocess defined in claim 2 wherein said particles consist of a resinselected from the group which consists of polystyrene and polyurethaneand said binder system comprises a water-insoluble binder componentselected from the group which consists of polymers of acrylic acid,homopolymers and copolymers of acrylic esters with vinyl esters,styrene, vinyl ethers, vinyl chloride and vinylidene chloride, a furtherbinder component serving as a flocculating agent for said chemisorbentand selected from the group which consists of polyacrylates, polyacrylicesters, acrylic esters copolymers, polyacrylamides and poly-ethyleneimines.